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question about marshall filter caps

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5/1/2000 3:27 PM

question about marshall filter caps

i have a couple questions about my marshall silver jubilee 50 watt. it has the usual 50/50 filter caps as most other marshalls i've had, but it also has a 3rd cap of the same type that is physically located away from the other 2. can someone look at this schematic and tell me what the extra cap i s for?
also, the amp is an 87 [only year they made them] and the caps are dated the same. it hasn't had much use, and it doesn't hum at all, so i want to know if theres any reason to replace the filters, and if so, what about that 3rd cap?

thanks,-dale

5/1/2000 3:51 PM
nigelbrew	If you are reffering to C34, that is the filter cap(s) for the preamp stages. I hope this helps. cheers, Nigel http://www.mp3.com/nigelbrewer http://clubs.yahoo.com/clubs/guitarampplayers

5/1/2000 4:12 PM
dale	why did they use that for the preamp tho? i mean, no other marshall i've had has had a 50/50/ 500volt cap in the preamp. dale

5/1/2000 4:20 PM
nigelbrew	It is probably more economical since they were using the same caps in the first filter stage and screen and driver supplies they could just punch one more hole in the chassis and order a higher qauntity of the same caps. This was pretty standard through the seventies and eighties. The JCM 900's have a single 33uf cap for the entire preamp, as do origional jtm45's

5/1/2000 4:45 PM

the 1959 and the 1986 has the 50/50 in the preamp section. i think i've read somewhere that you should filter caps between every set of 2 tubes when you step down the B+.
but if you look at the 1959 or 1986 they are putting filter caps every time they step down the B+.

i would think they are doing this mainly to block noise for the previous stages besides provideing a clean B+ or atleast that's my main thinking why they would be there i could be wrong.

5/1/2000 10:12 PM
Tonefactor	Q{why did they use that for the preamp tho? i mean, no other marshall i've had has had a 50/50/ 500volt cap in the preamp.} Most Marshalls made since the late 60's have this filter cap arrangement. All 2203/2204's and 1987/1959's have the 3 dual 50uf caps. The only Marshall I can think of that only use 2 of these dual caps is the 2205/2210.

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